Manufacture of coated board



Patented oeszz, 1946 UNITED STATE MANUFACTURE OF COATED BOARD Clark C. Heritage, Cloquet, Minm, asslgnor to Wood Conversion Company, Cioquet, Mlnn., a

corporation of pelaware No Drawing. Application September 9, 1939,

Serial No. 294,214

16 Claims. (Cl. 92-40) fibers are felted into a mat which is more or less porous.

Difiiculties are encountered in coating dry surfaces of porous board,-especially with aqueous coating compositions. Frequently, where the fibers are by nature absorptive of water, the board is made to be water-resistant when dry. Such dry boards repel aqueous coating compositions. The. coating of the dry board gives the coating materials but little chance to penetrate the surface, resulting in poor bond, substantial oil penetration and low resistance to washing. The interstices of a wet board are filled with water,- whereas the interstices of a dry board are filled 4 with air, so that upon a second dryin as after coating, the air is forced out and continuous coatings or complete coating of the individual fibers cannot be obtained by such a procedure. Other types of board. such as those of mineral fibers offer poor anchorage to such coatings, and air-entrapped in the pores keeps the composition from entering into the pores to improve anchorage. These resistances are highly apparent when a low usageot composition is employed to avoid filling the pores, and they become less apparent as a higher usage is employed in partially or wholly filling the pores.

In the case of wood or other vegetable fiber boards the fiber is usually treated to make a water-resistant dry board. Such boards are felted from a water suspension of fiber, in which an emulsion of a waterproofing agent such as oil, wax, i'at or insoluble metal soap; has been precipitated to deposit the agent on the wet fiber. Upon drying the fiber, as in the board-making process, the agent covers or permeates the fiber, rendering it resistant to re-wetting. Thus it is difficult to coat a fiber at the surfaceof the board, in order to hide the fiber completely. To effect hiding, a high usage of' composition is required which more or less buries or entraps the fiber, rather than coats it. v I A wood fiber board, and likewise other 1ignocellulose fiber boards, in their uncoated condition are unstable in appearance. There are photochemical changes in the coloring matter of the fiber, and a board may darken or lighten. This Y is very noticeable where panels of variegated colors are assembled in one wall. Eventually they become identical in color. These changes make it desirable to hide all the exposed fibers in coating a board. Completely covering the fibers per sewill prevent visible evidence of anychange which may occur, or it may prevent a. photochemical change. As covering is not complete, so will the change in color appear.

It is an object of the present invention to coat a fiber mat sufliciently completely to cover the fibers per se so that any change in color of the fiber is not visible.

It is another object of the invention to coat a fiber mat before it is dry using an aqueous coating composition.

It is a particular object of the invention to secure complete coverage of fibers with a minimum of pore-filling so as to present a board of stable fiber appearance comparable in texture to an uncoated board.

It is a further object to provide a water-resist: ant fiber board with a well-anchored coating applied as an aqeous composition. I

It is a further object of the invention to lock the surface fibers to the mat and to each other to prohibit detachment of fibers from the surface, to reduce filtering dirt out of passing air currents through fibers protruding, to provide a cleanable surface, and one resistant to marring.

It is a further object of the invention to use a coating composition on wet board in process oi! manufacture, and to dry the wet-coated board at an elevated temperature to yield a dry precoated board directly, having superior properties at lower usages.

It is a further object of the invention to provide a coated'boarcl with a composition which may vary in usage so as to provide a board of the same color appearance and varying appearances and textures according to the usage.

It is a further object of the invention to provide a wet coat on a Wet mat and. to dry the two together to avoid those forces which otherwise tend to warp the coated board when coated dry.

Various other and ancillary objects and advantages of the invention will be apparent from the following description and explanation of the invention. r

In the manufacture of board a slurry of fiber is formed to a. thick mat; which is dewatered by v gravity and then by vacuum, then pressed to remove more water, and eventually dried to a board. In the present invention it is desirable to apply a coating material before the board is dry, using such a composition as may safely or advantageously be subjected to the drying treatment,

or be improved or set by such treatment. An

aqueous coating composition is readily taken up by a wet board to wet the fiber where it is exposed on the 'surfaceand also within the pores. Be-

applied, depending upon the water-resisting prop-.

erties of the dry board. The presence of a waterproofing agent on the undried wet fiber, such as wax, precipitated from emulsion, does not prevent the ready wetting of the'wetfiber by an aqueous base composition. The composition may even fill pores if sufficient of it is present. This ready attachment of the composition effected through the mutual water contents, may take place when the water content of the board is 30% or more.

Desired coatings contain a pigmentor filler to provide hiding power, and the invention permits use of this hiding power to hide fibers with a low usage of pigment. I

The invention may be practiced with. many variations. It is not limited to any special coating composition so long as it has water as a contact ingredient. The term contact ingredient signifies herein that the composition at the surface is wet by water content, thus not including a composition of the water-in-oil type, which has a water ingredient. Thus, the composition and the wet fiber mutually wet each other, assuring good union, spreading, coverage, and adequate but not useless penetration, so that on drying the coat is well distributed and well anchored. Illustrative compositions are given below.

The coating composition may be applied in numerous ways, among them those which are suitable for webs made on continuous forming machines. For examples, the composition may be applied by doctor blade, spraying, or by roll. The use of a roll may be varied. Thus a roll may be set to compress slightly the mat to be coated, and a, pool of the composition lie in the nip of the roll on the mat. Also a roll may be coated with a film of the composition which is transferred to the web by contactwith the roll. The roll method requires compositions whichv do not exhibit higher adherence to the roll, and these are illustrated below.

The viscosity of the composition is a factor related to the character of the product obtained. A low usage may be practiced to effect coating the fibers exposed and leaving the pores apparently not changed, the fibers forming the pores at the surface of the pores being thoroughly coated.

A medium usage is permitted to effect thoroughly coating fibers and partially closing the pores.

A high usage is permitted to hide the location of the fibers as well as the fibers, and to seal the pores, making in effect a continuous coating in which fibers are embedded, the coating varying with the general level of the board, as distirfguished' from the local or detailed surface characteristics determined by fiber.

The wet mat surface may vary greatly to effect a desired general appearance of the board. It may be planar; it may be textured, as by irregular hills and valleys; or it may be embossed, specially or incidentally. Manyboards are incidentally embossed with screen-wire-marks as a result of theme of a screen wire in forming the mat. These marks may be coarse or fine, and even when fine, they are often more pronounced as viewed by the naked eye as markings than the pores themselves. Hence, the embossing from wires is usually visible after pores are sealed. However, the usage may be so high as to obliterate wire marks. Where embossing patterns are desired they are preferably made in the mat before coating and of size to remain visible in the type of product desired.

Where a roll or doctor blade application is desired, and the coated board is to present the irregular surface characteristics of the uncoated mat, it is an advantage of the process to use a wet mat. A dry mat or board having such characteristics is broken or crushed at the high spots in attempts to reach the low spots. But a wet mat so treated is resilient and yields in the high spots so that the application may reach the low spots.

The surface while wet and after coating may be calendered' by a roll, or brushed, to create a smoother surface. After drying, the surface may 'be calendered or brushed or even sanded to even out ro'ughness which may be inherent from the fiber surface, or the coat thereon, or both. In the coating of wet board there are severalother important characteristics. When the surface of the wet board is compressed in the presence of coating material the fibers are uniformly coated and the pores are in all probability filled. However, when the board passes out fromunder the action of the pressing roll the surface of the wet board springs back and sucks the coating deeper into the board coating fibers deep in the pores.

In the practical working out of the wet application there is a fine balance between the moisture content of the board, the bonding of the surface ofthe wet board, and the tackiness and viscosity of the coating mixture, all with respect to economical usage and satisfactory operation without rupture of the wet surface. These details must be worked out by those skilled in the art, as will be readily appreciated bythem.

Having thus explained the permissible variations the product may be described from several points of view. For such description, a wet mat of woodfiber with a wire-mark and with hills and valleys is referred to as a base to be coated. This has fibers which will exhibit color-change in a board dried directly from the wet mat. A white coating composition is referred to' as it affords strong contrast with the color of the fibers before or after change in color.

With a very light usage, such a board viewed under a binocular microscope has the same physical appearance as the uncoated board, except that the individual fibers are outstanding and white-coated. They appear as a brush-heap with deep recesses (pores) which are formed by white coated fibers. Th same board, viewed at close inspection with the naked eye, appears entirely white, open and porous, and of fibrous texture. The wire-marks are visible, and the hill and valley texture remains. Viewed from a distance,

as one would see it across a room, or on the ceiling, the board is rough-textured, and the wire- Using still ,more coating composition, the coat may be continuous and generally fiush with the upper layer of fibers, with the pores practically filled. The wire-marks may be partially filled, yet visible on close inspection. More composition may be applied until the wire marks disappear, and the surface assumes a smooth appearance lacking the form of individual fibers. Yet on distant inspection th texture of the hills and valleys will remain. A rough plaster effect is thus presented.

. The next stage beyond this is to use enough composition to fill the valleys and form a smooth surfaced board in which evidence of fiber body is practically lacking.

Compositions A wide variety of compositionshaving an aqueous component is available, Theemulslons of non-aqueous coating bases, such as nitro-cellulose, and the thermo-setting resins, may be used. Solutions of water-soluble resins may be used. Dispersions of hydrophilic colloids may be used. These are all employed to provide binder and vehicle for the covering pigment which provides the hiding power. Practically,the aqueous coating mixture may be any combination of water solutions, emulsions or suspensions. Practically, the pigment predominates in the solid content, the binder being relatively minor in proportion; The pigment may be chosen for economy and for color, and may be of mixed ingredients. Agents to assist in dispersing or smoothing the compositionmay be present. In actual practice pigment for white has been employed, to make a white board which exhibits no darkening. Pigments for "variegated color boards have been employed.

-- Both of these flll long-felt wants in the trade. Also resin-base coats have been used which are thermally set to present highly resistant properties. Several formulas are given by way of illustration. V

White coat The composition here given is more particularly described and claimed in the application of Heritage and Walter, Serial No. 294,215, filed September 9, 1939.

The borax is dissolved in the hot water and the protein dispersed therein. The boric acid solution is added to bring the protein dispersion to a value not over pH '7, such as pH 6.3, without precipitating the protein, so that on dryin it is not readily redispersible with water. Preferably, this is done-by adding a buffer agent or. some -nonvolatile constituent, which leaves a slightly acid condition. Ammonium salts may be used, which 6 williater lose ammonia, but these are desirably avoided on account of forming ammonia gas in the drier. Then the 'pigments are added. The diatomac'eous earth is required to give the proper covering power and uniformity at low usage, and.

' may be dispensed with at higher usage.

The viscosity is correct for applying from a pool behind a steel roller, as described. At a usage of 60 to 66 lbs. per 1000 square feet, the

l0 coating is continuous, wire marks are partly visible, pores are sealed, and the hill and valley texture shows. The wet coated board is dried at 310 F. to 345 .F. in an oven, which boils the.

water away. The escaping vapor makes a number of microscopic craters in the continuous coating, which is a characteristic result of the invention at a usage which forms a continuous coat.-

These are invisible to the naked eye. The drying equalizes tension so that the coated board has no tendency to warp due to the drying of the coat. This is in contrast to coating the same composition onto a dry board.

Variegated color There is a demand for. board in various shades of yellow-red tan, which may be indiscriminately 3 mixed as plank or tile. These have been provided' heretofore by natural fiber, or dyed fiber,

However, the color change of the fiber occurs, and, for example, behind a picture, the color becomes different than the color not covered in a wall. Variegated color specimens heretofore have so modified their colors by aging that they become substantially identical in color in a rela-z 5 tiveiy short time. One use of the present invention is to make a board with a surface having the natural fibrous textured uncoated appearance, 'yet in which individual exposed fibers are completely coated to make a light-fast surface. Thus, a variegated wall will remain such. Various similar compositions differing only in shade or tone are applicable to meet this demand, and are capable of such low usage that the board appears uncoated. I 5 Such compositions are represented as follows:

Parts by Common vehicle weight got water 170 F 1,000

max 17 -Protein (soy-bean) 100 Boric acid. v 10 Giycerine 10 Clay (white) 568 4 Color A Color B Color 0 Color D Red 1.0 0.75 1.30 0.85 Yellow 5.0 5. 25 4.70 5.00 Black 0.20 0.20 none The composition is used for the specified low usage effect in the amount of 42 pounds per 1000 square feet, by roll and pool ap lication, and the coated wet matdried at 310 F. to 345 F. in an oven. The product is a water-resistant board having the texture of an uncoated board with exposed fibers hidden by the pigment used. It resists the action of light to alter the color. The

color seen is that of the pigment, and not that of fiber. But the texture seen is the same as 'of the uncoated board. The composition here given is more particularly described and claimed in the application of Heritage, Walter and Sedoif,

Serial No. 294,216, filed September 9, 1939.

Resin coat The use of a thermosetting resin, and the use of an emulsion, as distinguished from a protein dispersion, as a binder, is shown in the following Aquaplex A-90 is a trade-marked product made by Resinous Products 8: Chemical Co., Inc. of Philadelphia, Pennsylvania, and is a glycerolphthalic-anhydride condensation productcarried in aqueous emulsion of 40% solids, which sets to a resin by thermal action, or upon drying. It may beapplied in various ways, and as compounded above, the composition is suitable to application from a pool by a roll. At a usage of 57 lbs. per 1000 square feet, it, produces a continuous coat when dried at 310 to'345" F.

The above resin composition is disclosed in my copending application Serial No. 294,213, filed September 9, 1939.

Fiber positions are visible microscopically, and the pores are sealed. There are formed the characteristic microscopic craters. ting of the resin gives high resistance to washing, and various cleaning agents, and great durability. The pigment may of course be changed. The resin base is far more costly than the protein base, and therefore in practice, the protein base is preferred.

It is therefore to be understood that the compositions may have other bases, such as starch,

casein, glue, phenolaldehyde resins, alkyd resins,

cellulose derivatives, and other well known binders which dissolve in water, or are emulsifiable or dispersible in water, and which when so carried are able to hold dispersed pigments.

In the case of the soy-bean protein, the high heat of the drying setsit to a harder and more resistant bond than when the same is air dry. In air-drying the lithopone coating, the surface is chalky, because the bond is weaker. Likewise, the resin coat is set by the heat. Therefore, in choosing the binder, it is preferred to use one which is benefited by the high heat of the drying chamber above the boiling point which the board is dried.

This drying produces distinctive bonds. In the coating pigment particles are bonded to each other by the binder. At the interface of fiber and coating, pigment particles are bonded to fiber by the binder. At and below the pigment line, fiber is bonded to fiber by binder diffused into the board. This last is in addition to the bond of fiber to fiber which exists throughout of water, at

the body of the board. The dispersion of the binder in the composition, and the mutual wetting of the mat and the composition, carry binder somewhat into the board to aid in binding the fibers to fibers in the vicinity of the surface of the mat. Thus, the surface of the board proper is hardened or toughened even by a low usage.

It is a practice in making boards to add binder, filler or sizing material to the stock so as to leave the same in the finished board, for example, a col- The thermal set-.

loidal starch. This may be done with the stock of which the mat is to be coated, without in any way interfering with the invention as described. Also, where such filler is or is not present, the surface of the wet mat may be sized with the same effect by wetting the formed board with a thickened sizing solution, such as gelatine or other-protein, or starch or the like. This penetrates into the surface for a limited distance, so that on drying the board, the so-treated surface is harder and more resistant to scuff. Such size more readily enters the board than the coating composition with its load of pigment. By using such size preliminarily to using the composition, more of the binder of the composition remains in the pigment coat. Thus, where a more expensive binder, such as synthetic resin is employed, its

. quantity may be reduced. A starch solution (thick-boiled as in laundering) may be used as an undercoat, filling the pores and sizing the fibers, and while the board is still wet with such starch solution, the pigmented aqueous composition may be applied, as if no sizing were present.

111 the specification and accompanying claims where reference is made to binding the particles of pigment to the fiber, it is to be understood that the fiber may be sized before or after the mat is formed, as described, or not at all.

From the foregoing it will be understood how the invention may be varied within the scope of the appended claims.

I claim:

1. The method of making a coated rigid porous structural fiber board which comprises coat-- ing a wet structural-board-forming mate of fibers with a composition having sufllcient pigment to hide the surface fibers and having also an aqueous vehicle in which is carried a binder capable of binding the pigment to the "fiber and to itself upon loss of the vehicular water, and drying the mat and the coat thereon simultaneously to form the board.

2. The method of making a coated water-resistant rigid porous structural vegetable fiber board which comprises forming a water slurry of wet vegetable fibers carrying a Water-proofing agent deposited thereon, forming said slurry into a wet structural-board-making mat, coating said wet mat with a composition having sufiicient pigment to hide the surface fibers and having also an aqueous vehicle in which is carried a binder capable of binding the pigment to the fiber and to itself upon loss of the vehicular water, and drying the mat and the coat thereon simultaneously to form the board.

3. The method of making a coated rigid porous structural fiber board which comprises coating a wet structural-board-forming mat of fibers with a composition having sufficient pigment to hide the surface fibers and having also an aqueous vehicle in which is carried a binder capable of binding the pigment to the fiber and to itself upon loss of the vehicular water, and drying the mat of wet vegetable fibers carrying a water-proofing agent deposited therein, forming said slurry in a wet structural-board-making mat, coating said wet mat with a composition having suflicient pigment to hide the surface fibers and having also an aqueous vehicle in which is carried a binder capable of binding the pigment to the fiber and to itself upon loss of the vehicular water,

tinuous coat with pore openings into the mat and with coating material over all the surface fibers.

6. The process of claim 2 in which the composition is applied in quantity to form a discontinuous coat with pore openings into the mat and with coating material over all the surface fibers.

7. The process of claim 3 in which the composition is applied in quantity to form a discontinuous coat with pore openings into the mat and with coating material over all the surface fibers.

8. Theprocess of claim 4 in which the composition is applied in quantity to form a discontinuous coat with pore openings into the mat and with coating material over all the surface fibers. i

9. The process of claim 1 in which the composition is applied in quantity toform a continuous coat with substantially all the pores of the mat sealed.

- slightly, holding a pool of aqueous coating come 10. The process of claim 2 in which the composition is applied in quantity to form a continuous coat with substantially all the pores of the mat sealed.

11. The process of claim 3 in which the composition is applied in quantity to form a continuous coat with substantially all the pores of the mat sealed.

12. The process of claim 4 in which the composition is applied in quantity to form a continuous coat with substantially all the pores of the mat sealed.

13. The process of claim 1 in which the composition is applied in quantity to form a continuous coat sealing substantially all the pores of the mat but not filling them, whereby the forms of individual hidden fibers are distinctly visible at the surface of the mat upon magnification.

14. The method of forming a coated porous structural board, which comprises forming a wet structural-board-forming mat by felting from an aqueous slurry of fibers, said mat being such as to form a rigid porous board on drying. Passing said mat under a roll set to compress the surface slightly, holding a pool of aqueous coating composition behind said roll whereby a limited portion enters the board surface and whereby an excess is squeezed outin passing under the roll in accordance with the degree of compression of the wet mat, thereby leaving a limited amount of the aioaeae Y l0 composition adherent to the fibers exposed at the surface and visible within the surface pores of the mat, and drying the resulting mat whereby the residual coating composition dries with anchorage to said fibers, lesser-and greater compression of the mat by the roll respectively leaving more and less composition at the surface whereby excess over that required to hide the fibers tends to close the pores by drying in capillary spaces between adjacent and crossing fibers in the surface of the board.

15. The method of forming a coated porous structural board, which comprises forming a wet structural-board-fcrming mat by felting from an aqueous slurry of fibers, said mat being such as to form a rigid porous board on drying, passing said mat under a roll set to compress the surface position behind said roll whereby a limited portion enters the board surface and whereby an excess is squeezed out in passing under the roll in accordance with the degree of compression of the wet mat, thereby leaving a limited amount of the composition adherent to the fibers exposed at the surface and visible within the surface pores of the mat, and drying the resulting mat whereby the residual coating composition dries with anchorage to said fibers, lesser and greater compression of the mat by the roll respectively leaving more and less composition at the surface fibers tends to close the pores by drying in capillary spaces between adjacent and crossing fibers in the surface of the board, the compression of the mat by the roll being such as to effect a compression of the lower areas in the surface of the mat, whereby excess liquid in the mat from the pool is squeezed from the entire surface of the mat. 1

$16. The method of forming a coated rigid porous structural fiber board which comprises covering the surface of a wet structural-boardforming mat with a mass of aqueous pigmented A liquid coating composition-containing a dispersed binder which dries to bond the pigment to itself and to fibers, the mat being wet with water throughout and having microscopically upstanding fibers with resilience at the surface, and pores between them, pressing the wet coated mat to compress the body of the mat,' releasing the compressed mat whereby the fibers carrying adherent coating composition spring away from the body of the board and the pores tend to suck in excess of the composition, whereby the surface fibers are coated with the liquidcomposition and pores remain open, and drying the wet mat with heat to form a rigid porous coated board.

CLARK C. HERITAGE.

Certificate of Correction 1 Patent No.2,409,628. October 22, 1946. CLARK C. HERITAGE It is hereby certifiedthat errors appear in the printed specification of the above numbered patent requirin correction as follows: Column 8, line 35, claim 1, for mate read mat; line 71, c aim 4, for therein read thereon; line 72, same claim 4, for

in read into; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

signed and sealed this 28th day of January, A. D. 1947.

LESLIE FRAZER,

First Assistant Commissioner of Patents. 

